[WIP] Title annotation

This is work-in-progress. It is being implemented on top of https://github.com/xtannier/WebAnnotator/pull/4, so there is a lot of extra commits until #4 is merged. 

TODO:

* [ ] extra toolbar buttons
* [ ] "annotate title" button
* [ ] "annotate title" menu items
* [ ] title editing HTML popup
* [ ] saving title markup
* [ ] loading title markup
* [ ] better icons